[Haskell-cafe] (liftM join .) . mapM

[Stephen Tetley]

2009/12/29 David Menendez <dave at zednenem.com>:

> Why restrict yourself to functions? You can generalize this to
> arbitrary stacks of functors.
>
> oo :: (Functor f, Functor g) => (a -> b) -> f (g a) -> f (g b)
> oo = fmap . fmap

Hi David

Nice! this seems to be taking things into TypeCompose territory, cf. fmapFF.

http://hackage.haskell.org/package/TypeCompose


For my purposes, I do like the simple (functional) type signatures of
the original specs combinators, but maybe they are under-utilizing
good names on something that merits being more general...

Best wishes

Stephen